rename locales to Weblate locales

[bozana]

We have just merged this issue pkp/pkp-lib#9707 that aligns PKP locales with Weblate locales (s. https://github.com/WeblateOrg/language-data/blob/main/languages.csv). I am going through the plugins from the PKP plugin gallery (for 3.4 release) and will inform the maintainers if they would need to rename the plugin locales for 3.5 (coming in the first quarter of 2025).
If this plugin is going to be made compatible with the coming release 3.5 the locales renaming would be needed. The locale fr_FR needs to be renamed into fr.

[ajnyga]

thanks!